[Avodah] A Question About Davening Vo'Sikin

[Micha Berger]

On Wed, Mar 18, 2009 at 03:48:59PM -0400, Rich, Joel wrote:
:                                                        Do local weather
: conditions change the time of [ha]netz?) or is [ha]netz really defined
: objectively and  we try to approximate as best we can in each generation
: based on the tools and knowledge we have.

My understanding is that "visible" is usually defined by the common
person, not the individual. A nearly blind person isn't allowed to
eat thrips. So, there is an objective definition.

That said, weather does influence haneitz. It changes the refraction
index of the air, and therefore the bend it gives light. (It also
changes the density gradient and therefore where the bending occurs.)

As I recently wrote to Areivim:
> When light enters the atmosphere, it bends. The same thing that makes a
> spoon that is sticking out of a glass of water look bent at the point
> where it enters the water. (It's also why the sun loses about 1/6
> its height when just at the horizon, looking like an oval. That's the
> difference between the 34' (34/60 deg) refraction at the horizon vs the
> 29' refraction at the top of the sun.)

> Every 3 degC / 5.4 degF translates to around 1.35 sec change in the
> motion of the sun at the horizon. As does every .9 kPa pressure. So,
> you're given the time of sunrise if it were 10degC = 50degF. If the
> temperature goes up to 26degC (79degF) and the air pressure is still
> sea level norm, the error would be 21 sec.

> At sunrise in Passaic [yesterday], the air temp was 36 degF, the pressure
> was 30.31". That means that the air pressure contributed 4 sec and temp
> added 10.5 sec. Total error compared to even the best formula was over
> 14 sec.

Is it subjective? Well, it's experiential rather than astronomical -- then
the sun looks like it's crossing the horizon. But it's the experience of
the typical person, not of the subject in question. I think I'll avoid
getting into a technical debate as to whether that's called "subjective".

-Micha

PS: A netz is a bird of prey (hawk [LXX, Rashi], gosshawk [Tosafos, Arukh,
Radaq], and RNS probably thinks it's some third species). I could argue
that that kind too is defined experientially rather than by zoological
taxonomy (species), but that would be too far off topic. I think you mean
haneitz, with a leading qamatz-hei, the hif'il. "The causing to sparkle"
of the sun. LHQ is qodesh; we should consider using it accurately as
something precious.

-- 
Micha Berger             "'When Adar enters, we increase our joy'
micha at aishdas.org         'Joy is nothing but Torah.'
http://www.aishdas.org    'And whoever does more, he is praiseworthy.'"
Fax: (270) 514-1507                     - Rav Dovid Lifshitz zt"l